Modern day automobile engines have become sophisticated machinery controlled by computers to handle virtually all aspects of the operation of the vehicle. In recent years, the control over various aspects of the engine have increased to the point where almost every movement or operation of the engine is governed or monitored by a computer. The present invention relates to a particular aspect of the engine's operation under the control of the vehicle's onboard computer, or engine control unit (“ECU”).
One key characteristic of a vehicle's engine is the power generated by the engine, which is a function of the degree and extent that the intake and exhaust valves open, how long the stay open, and the timing of when they open and close. If the valves open slightly longer and/or a slightly later in the ignition cycle, or if they are opened for a prolonged portion of the cycle, the engine will exhibit a distinct muscle-car rumble with an accompanying high-rpm horsepower. Conversely, reducing the opening of the valves and opening them slightly earlier results in a smoother engine percussion with a steady idle, good low-rpm torque, superior fuel economy and lower emissions. Traditionally, the control of the valve movements and timing in all aspects have been controlled by a camshaft with carefully calibrated lobes that pushed the valves open at exactly the right time and maintain the opening for the desired duration.
In today's engines, camshaft phasers play an important role in a key aspect of the cam timing: the camshaft's position relative to the crankshaft, and thus the position of the pistons connected to it. If one advances or retards the cam slightly relative to the crankshaft, the valves will open and close sooner (or later) relative to the piston coming up in the bore. When the cam advances earlier, the engine will sound smoother but will lack top end horsepower. “Retarding” the cam, i.e., turning it so the valves open and close late, is better for horsepower but results in what some consider to be an overly loud, disruptive noise (albeit one that some vehicle owners prefer). Traditionally, engine manufacturers set a certain amount of cam advance or retard while designing the engine. This could be accomplished by moving the whole cam sprocket gear one tooth forward or backward on the timing chain, or through aftermarket adjustable sprockets that could be rotated relative to the camshaft's original position.
A cam phaser is an adjustable camshaft sprocket mounted on the chain, and can be turned by means of a computer-controlled solenoid. Rather than pre-setting a certain amount of advance or retard, the computer can advance the cam or cams in situ at low rpm to enhance driveability, and retard the cam or cams at high rpm for more horsepower. Cam phasers may be specially designed for a particular engine, and computer-controlled cam gears for specific engines have the ability to adjust camshaft position (and thus valve opening and closing) while the engine is running. In the case of Ford modular engines that use two camshafts, two cam phasers are used. To actuate the cam phaser, engine oil is pressure fed to the cam phasers through a series of passageways in the cylinder heads and camshafts. The engine computer controls a pair of solenoids that adjusts this oil flow into and out of the cam phaser's control chambers, giving the ability to retard the cams in some cases up to 60 degrees or crank rotation.
When the cams are retarded approximately 20-40 degrees during part throttle engine operation, it takes less power to turn the engine over. This helps to increase the engine's fuel efficiency. Another power benefit is that the cam phasers allow the camshafts to always be in the optimal position for maximum power, regardless of what the engine's rpm is. The engine thus in able to generate more torque and horsepower and extends the high rpm powerband by, in some cases, an extra 800-1000 rpm.
However, one downside of stock cam phasers it is that they are exceptionally sensitive to changes, specifically the reduction of, oil pressure. Since the cams can theoretically be retarded by up to 60 degrees, when an issue arises, it causes the cam phaser to no longer have controlled movement. This can cause “knocking” or excessive engine noise if there is interference between the cam and the piston. This minimal piston to valve clearance also limits most engines to fairly small cam profiles with very little overlap. Thus, a solution is needed to address the issue of excessive movement with inadequate clearance due to the wide range of movement resulting from the camshaft phaser. In addition to this, the rapid, and violent action of the cam phaser moving from each end of the mechanical limit without control can cause the cam phaser to separate from the camshaft causing severe engine damage.